The present invention relates to a semiconductor apparatus having a trench Schottky barrier Schottky diode. A semiconductor apparatus of this kind in the form of a trench Schottky barrier Schottky diode is described in German Patent Application No. DE 10 2004 059 640 A1, and has a semiconductor volume of a first conductivity type, which semiconductor volume has a first side covered with a metal layer, and at least one trench extending in the first side and at least partly filled with metal.
Schottky diodes usually have metal-semiconductor contacts or silicide-semiconductor contacts. In Schottky diodes, high injection does not occur in forward mode, and clearing of minority charge carriers at turn-off is therefore absent. They switch comparatively quickly and with little loss. The term “high injection” refers here to a state in which the density of injected minority charge carriers approaches the order of magnitude of the majority charge carriers.
Schottky diodes have relatively high leakage currents, however, especially at high temperature, with a strong voltage dependence due to the “barrier lowering” effect. Thick and lightly doped semiconductors are also generally needed for high reverse voltages, resulting in comparatively high forward voltages at high currents. Power Schottky diodes using silicon technology are therefore, despite good switching behavior, poorly suitable or unsuitable for reverse voltages above 100 V.
The semiconductor apparatus according to the present invention differs from the existing art, and is notable for at least the fact that at least one wall segment of the trench, and/or at least one region, located next to the trench, of the first side covered with the metal layer, has a layer, located between the metal layer and the semiconductor volume, made of a first semiconductor material of a second conductivity type.
The example trench Schottky barrier Schottky diode according to the present invention (hereinafter also referred to as a “TSBS-P” or “TSBS-PN-P” or “diode,” as will be further explained below) makes possible a comparatively low forward voltage and comparatively low switching losses. The comparatively thin layer of the first semiconductor material of the second conductivity type furthermore enables additional shielding of a Schottky contact constituted by use of the metal layer. The result is that reverse currents can be appreciably reduced, in particular at high temperature, while forward voltages and switching losses remain comparatively low.
The layer, disposed in this fashion, made of the first semiconductor material enables particularly low forward voltages in the range of high current densities as compared with conventional high-voltage Schottky diodes, since the conductivity of the semiconductor volume is greatly elevated by high injection. This advantage can be further enhanced by way of an integrated PN diode. In addition, the layer, disposed in this fashion, made of the first semiconductor material results in comparatively low leakage currents thanks to shielding of the Schottky effect with the aid of the trench structure. This is furthermore suitable for modifications that yield comparatively good robustness thanks to a voltage-limiting clamping function of an integrated PN diode.
As compared with conventional high-voltage PiN diodes, the advantage of a comparatively low forward voltage at high current density is obtained with the aid of a suitable Schottky contact barrier height in combination with high injection at high current density. Comparatively low turn-off losses are also obtained, since in forward mode fewer charge carriers are injected into and stored in the low-doped region as a result of the Schottky contact system (e.g., Schottky contact in combination with a thin p-layer directly beneath the Schottky contact). As compared with further conventional “cool SBD” diodes, lower forward voltages at high current density occur thanks to more intense high injection, and lower leakage currents are obtained as a result of effective shielding of the Schottky effect.
As compared with a conventional TSBS or TSBS-PN not having a semiconductor layer disposed in this manner (located, for example, as a thin p-layer directly beneath the Schottky contact), particularly low leakage currents are obtained along with a lower forward voltage at high current density, with somewhat higher turn-off losses. In embodiments having an integrated PN diode, particularly low leakage currents are obtained with almost the same forward voltage at high current density, and almost identical turn-off losses.
Advantageous embodiments are described below and are shown in the figures. The features can be advantageous both in isolation and in various combinations even though further reference thereto is not explicitly made.
It is possible to embody the diode according to the present invention in such a way that a breakdown voltage of the diode is, for example, higher than 10 volts, in particular higher than 100 volts, in particular higher than 200 volts, or in particular even higher than 600 volts. The Schottky diode according to the present invention is thus suitable in particular for high-voltage utilization, and at the same time has a low forward voltage, a low leakage current, and low switching loss, and is highly robust. The Schottky diode according to the present invention can furthermore advantageously be used in particular as a power diode for inverters, for example for photovoltaics or automobile applications. For example, the diode can also be used as a so-called “freewheeling” diode.
In an embodiment of the semiconductor apparatus, the semiconductor volume has at least two trenches. The advantageous properties of the trench Schottky barrier Schottky diode can thereby be further improved.
Provision can furthermore be made that the first semiconductor material of the second conductivity type has a layer thickness in a range from 10 nm to 500 nm. Provision can moreover be made that a doping concentration of the first semiconductor material of the second conductivity type is in a range from 1016 atoms per cubic centimeter to 1017 atoms per cubic centimeter. Thin layers of this kind, in particular together with the doping concentration indicated, are particularly suitable for enabling a comparatively low reverse current, a comparatively low forward voltage, and comparatively low switching losses for the diode according to the present invention.
In an example embodiment of the present invention, a region of a bottom of the at least one trench is filled with a second semiconductor material, the second semiconductor material being a polycrystalline semiconductor material of a second conductivity type or a semiconductor material of the second conductivity type. This is preferably accomplished in such a way that a PN diode is formed by way of the second semiconductor material and the semiconductor volume of the first semiconductor type. It thereby becomes possible to integrate a PN diode (a so-called “clamping” element) into the semiconductor apparatus according to the present invention, electrically in parallel with the trench Schottky barrier Schottky diode.
In an embodiment of the invention, a breakdown voltage of the PN diode is lower than a breakdown voltage of the trench Schottky barrier Schottky diode constituted by the metal layer, by the layer of a first semiconductor material of the second conductivity type, and by the semiconductor volume of the first conductivity type.
Preferably, the semiconductor apparatus is embodied in such a way that an electrical breakdown can occur in a region of the bottom segment of the at least one trench.
Preferably, the semiconductor apparatus is embodied in such a way that it can be operated in a state of breakdown with comparatively high currents.
In an example embodiment of the present invention, the region of the bottom of the at least one trench is converted, by ion implantation of boron (generally: of dopant of a second conductivity type at a higher concentration than that of the first conductivity type), to a semiconductor material of the second conductivity type. The overall properties of the semiconductor apparatus can thereby be improved.
Provision can furthermore be made that the trench at least partly filled with metal has at least two metal plies disposed above one another with respect to a depth of the trench, an upper metal ply forming a segment of the metal layer with which the first side of the semiconductor volume of the first conductivity type is covered, and the metal plies preferably encompassing different metals. Preferably the at least one trench is completely filled with at least one metal.
Provision can be made in supplementary fashion that a height of a potential step (Schottky barrier) of the upper metal ply, which corresponds to the metal layer, is lower than a height of a potential step (Schottky barrier) of a metal ply disposed therebeneath. The result is to produce a plurality of further advantageous possibilities for improving the properties of the trench Schottky barrier Schottky diode and adapting them to particular electrical requirements.
In a further example embodiment of the semiconductor apparatus, a second side of the semiconductor volume, which is located oppositely facing away from the first side covered with the metal layer, is covered with an electrically conductive contact material, and a partial volume, adjacent to the contact material, of the semiconductor volume is more highly doped than the remaining semiconductor volume. The partial volume is, in particular, a so-called “n+” substrate (with inverse doping of the semiconductor apparatus it is a “p+” substrate), as is similar fashion in the related art. The metal layer described above can be used as a first electrode (anode electrode) and the aforesaid contact material (which preferably is likewise embodied as a metal layer) can be used as a second electrode (cathode electrode). The overall result is to describe a particularly suitable configuration for the diode according to the present invention.
In an example embodiment of the semiconductor apparatus according to the present invention, it has solderable electrodes or solderable component terminals.
In an example embodiment of the semiconductor apparatus, it is embodied as a press-in diode and has a corresponding housing. Provision can be made in supplementary fashion that the semiconductor apparatus is an element of a rectifier assemblage for a motor vehicle.
Provision can furthermore be made that the semiconductor apparatus is manufactured at least in part using an epitaxy method and/or using an etching method and/or using an ion implantation method. Advantageous possibilities for manufacturing the semiconductor apparatus according to the present invention are thereby described.
In a further embodiment of the semiconductor apparatus, a depth of the at least one trench is from 1 μm (micrometer) to 4 μm, preferably is approximately 2 μm. This configuration yields particularly suitable dimensions, for example, for use of the diode according to the present invention for a rectifier assemblage in motor vehicles. For example, an allowable reverse voltage of approximately 600 volts can be achieved for the diode according to the present invention. A further advantageous configuration of the semiconductor apparatus is obtained if a ratio of a depth of the trench to a clearance between each two trenches is greater than or equal to approximately 2.
Provision can furthermore be made that the at least one trench has substantially a ribbon shape and/or substantially an island shape. The ribbon shape describes a substantially elongated shape (line) and the island shape describes substantially a concentrated shape, in particular a circular shape, hexagonal shape, or the like. Preferably the trench has a substantially rectangular cross section. A bottom of the trench can be embodied to be flat or rounded (“U” shape), for example semi-spherical.
In a first variant of the semiconductor apparatus according to the present invention, the first conductivity type corresponds to an n-doped semiconductor material and the second conductivity type corresponds to a p-doped semiconductor material. In a second variant of the semiconductor apparatus according to the present invention, the first conductivity type corresponds to a p-doped semiconductor material and the second conductivity type corresponds to an n-doped semiconductor material. The semiconductor apparatus is thus suitable in principle for both possible polarities.
Provision can furthermore be made that the semiconductor apparatus encompasses a silicon material and/or a silicon carbide material and/or a silicon-germanium material and/or a gallium arsenide material. The invention is thus applicable to all usual semiconductor materials.
Exemplifying embodiments of the present invention are explained below with reference to the figures.